Embodiments of the invention relate generally to a micro-electromechanical system (MEMS) switch.
Microelectromechanical systems (MEMS) generally refer to micron-scale structures that can integrate a multiplicity of functionally distinct elements such as mechanical elements, electromechanical elements, sensors, actuators, and electronics, on a common substrate through micro-fabrication technology. MEMS generally range in size from a micrometer to a millimeter in a miniature sealed package. A MEMS switch has a movable actuator that is moved toward a stationary electrical contact by the influence of a gate or electrode positioned on a substrate.
FIG. 1 illustrates a conventional MEMS switch in an open or non-conducting state according to the prior art. The MEMS switch 10 includes a substrate 18, a movable actuator 12, a contact 16 and control electrode 14 mechanically coupled to the substrate 18. In operation, the movable actuator 12 is moved toward the contact 16 by the influence of a control electrode 14 (also referred to as a gate or gate driver) positioned on the substrate 18 below the movable actuator 12. The movable actuator 12 may be a flexible beam that bends under applied forces such as electrostatic attraction, magnetic attraction and repulsion, or thermally induced differential expansion, that closes a gap between a free end of the beam and the stationary contact 16. The movable actuator 12 is normally held apart from the stationary contact 16 in the de-energized state through the spring stiffness of the movable electrode. However, if a large enough voltage is provided across the stationary contact 16 and the movable electrode 12, a resulting electrostatic force can cause the movable electrode 12 to self-actuate without any gating signal being provided by control electrode 14.
Power system applications of MEMS switches are beginning to emerge, such as replacements for fuses, contactors, and breakers. One of the important design considerations in constructing a power switching device with a given overall voltage and current rating is the underlying voltage and current rating of the individual switches used in the array of switches that comprise the device. In particular, the voltage that the individual switches can withstand across their power contacts is an important parameter. There are several factors and effects that determine the voltage rating of an individual MEMS switch. One such factor is the self-actuation voltage.
In a MEMS switch, the self-actuation voltage is an effect that places an upper bound on the voltage capability of the switch. Electrostatic forces between the line and load contacts (e.g. between the movable actuator and stationary contact) will cause the movable actuator to self-actuate or make contact with the stationary contact when the voltage between across the actuator and contact exceeds a certain threshold. In certain current switching applications, this self-actuation can result in catastrophic failure of the switch or downstream systems.